The present invention concerns avionics networks. More particularly, but not exclusively, this invention concerns an aircraft control system for an aircraft comprising an avionics network and related components/parts and associated software. The invention also concerns a method of operating and/or reconfiguring such an aircraft control system, and a method of communicating across an avionics network. The invention also concerns an interface unit configured for use as the interface unit.
With the advent of the “digital aircraft” there has been a drive to improve the integration of modern digital networking concepts with the analogue sensors and actuators that remain as standard in the aircraft industry and to take advantage of the opportunities that arise with the use of data networking in the aircraft.
Airbus has for example developed its own networking standard for handling of data in an aircraft, which is referred to by Airbus as “AFDX”. Airbus' AFDX network is a switched full duplex network based on Ethernet network technology (based on the IEEE 802.3 standard). AFDX networks are typically fully compliant with Part 7 of ARINC 664 (one of the standards provided by Aeronautical Radio, Incorporated or “ARINC”). The term AFDX is used by Airbus as a trade mark but the technical characteristics of an AFDX network are well-defined and understood by those skilled in the art. The term “AFDX” alludes to the main characteristics of the network—i.e. one that is specifically designed for Avionics and is a Full DupleX network.
The present application is concerned primarily with the use of, and improvements to, such avionics networks, particularly networks compliant with Part 7 of ARINC 664, and parts thereof, in the context of commercial airliners, although there may be applications in other fields of avionics such as transport/freight aircraft, military aircraft and the like.
U.S. Pat. No. 6,925,088 has been cited as an Airbus patent that concerns Airbus' AFDX network technology, but there are various patents that relate to AFDX networks and related concepts. U.S. Pat. No. 6,925,088 itself concerns an avionics network including subnets of peripheral units (such as computers, closed loop controllers, and the like) each subnet being connected by a star distributor implemented in the link layer (of the OSI model). The star distributor facilitates direct communication between the peripheral units on the subnet using MAC addresses on the link layer. Periodic and aperiodic data communication is also discussed, as is the use of an Ethernet-type network in such a way that negates the need for collision detection. The invention of U.S. Pat. No. 6,925,088 assists in the use of commercially available data busses (outside the avionics field) with avionics data busses specifically developed for aircraft applications.
U.S. Pat. No. 7,242,683 (related to U.S. Pat. Nos. 7,339,901 and 7,352,744) mentions the use, in the civil aeronautics field, of ARINC 429-based avionics networks and the desire to integrate with Ethernet-type networks. U.S. Pat. No. 7,242,683 recognises the need in avionics networks for segregation of data flows and for providing reliable (guaranteed) data transfer performance (in terms of network access, latency, etc.) for certain avionics applications. U.S. Pat. No. 7,242,683 discloses an AFDX network in the form of an avionics-compatible deterministic switched full-duplex Ethernet-type network utilising Ethernet-type data frames. (U.S. Pat. No. 7,242,683 defines the term “full-duplex” as meaning that the subscriber can send and receive packets at the same time on the same link and the term “switched” as meaning that the packets are switched in switches on appropriate outputs. “Deterministic” as used here means that the network guarantees certain things such as network access, latency, bandwidth and logical segregation of certain data flows). In particular, U.S. Pat. No. 7,242,683 discloses the concept of virtual links within the AFDX network. Thus, there is disclosed an AFDX network having source subscriber equipment and destination subscriber equipment connected to each other via a physical link incorporating a network switch and connected via a virtual link. The virtual link is defined as the conceptual representation of a link (over the data link layer—layer 2 of the OSI model) from the source equipment to the destination equipment, in which the Ethernet-type frames transmitted provide for segregation between virtual links and allocation of a fixed passband for each virtual link. Virtual links are multiplexed, by means of the data frames (there typically being a sequence of Ethernet frames, each frame being associated with a single virtual link) over the physical link layer. It will be understood of course that “subscriber equipment” will typically comprise one or more sensors/actuators that are connected to the AFDX network by means of a network terminal that forms part of the subscriber equipment, the equipment thus including an appropriate interface (encoding/decoding equipment) which converts between analogue signals native to the sensor(s)/actuator(s) and the data frames used on the network. Each such item of subscriber equipment will be designed for the specific application to which the actuators/sensors are to be put on the aircraft. Some items will require more data processing than others, and some items may require analogue-to-digital converters (ADCs) and no digital-to-analogue converters (DACs), whereas others may require DACs and no ADCs. The processing and memory requirements vary from one type of equipment to another.
U.S. Pat. No. 8,503,439 proposes connecting a subscriber (comprising sensors/actuators) to an AFDX network by means of a frame switching device being located locally to the sensor/actuator equipment to which it is connected. Having a network in which there are several local switches, as opposed to connecting each item of sensor/actuator equipment to a respective frame switch in a centrally located avionics IT rack, has the potential benefit of reducing the amount of wiring needed to connect the sensors/actuators. Each item of sensor/actuator equipment is configured for digital data communication with its local switch device and is arranged to receive/transmit data frames. The local switch device thus has a first port connected to the AFDX network (to a switch of the network or to a terminal) and one or more second ports connected to the items of on-board sensor/actuator equipment. U.S. Pat. No. 8,503,439 proposes polling (sampling) data frames on ports of the local switch, periodically and in turn, and replicating such frames onto other ports of the local switch. The local switches proposed in U.S. Pat. No. 8,503,439 have been developed further and are now generally referred to as AFDX micro-switches. The polling and copying functions mentioned above provide that the AFDX micro-switches have a hub function over the downlink and a switching function over the uplink. The term μAFDX-network (micro AFDX network) has been used to refer to the network (or subnet) that comprises an AFDX micro-switch and the items of sensor/actuator equipment connected via that AFDX micro-switch to the rest of the avionics network.
U.S. Pat. No. 8,600,584 concerns an aircraft control system in which different avionics software applications associated with different aircraft functions can share one or more sensors via an AFDX network. U.S. Pat. No. 8,600,584 also discloses the use of data concentrator devices for connecting multiple subscribers to an AFDX network. Specifically, U.S. Pat. No. 8,600,584 describes a network configuration in which measurements provided by sensors are acquired, multiplexed, and converted into AFDX messages by remote data concentrators before being passed onto the AFDX network for receipt by a central computer which runs the avionics software applications. Control messages are received by local control units which are each configured to convert AFDX messages into control signals for receipt by the actuators connected to the local control unit. The sensors connected to such remote data concentrators are available for use by different avionics applications. As such the remote data concentrators are a shared resource on the AFDX network.
US 2013/156427 concerns the extension of an AFDX network (in which, as described above, subscribers to the AFDX network are each directly connected to a switch of the network, and in which data is transmitted as IP packets encapsulated in Ethernet-type frames having virtual link identifiers). It is recognised in US 2013/156427 that AFDX micro-switches enable the AFDX network to be extended so that additional/remote items of equipment can access it (i.e. by means of the AFDX micro-switch being connected directly between a frame-switch of the AFDX network and the items of equipment and functioning as described above, so that frames received on the downlink are replicated to all the items of equipment and any frame received over the uplink from any item of equipment is forwarded to the AFDX frame-switch to which AFDX micro-switch is connected). US 2013/156427 proposes the extension of the AFDX network by means of a passive optical network (“PON”) that sits between the AFDX network backbone and at least some of the items of on-board sensor/actuator equipment. US 2013/156427 also proposes a μAFDX (micro AFDX).
US 2014/180504 concerns an aircraft control system utilising an AFDX network. There is provided a central computer which has MONitoring (“MON”) and COMmanding (“COM”) modules which communicate with items of remote equipment (such equipment including actuators/sensors) subscribed to the AFDX network over virtual links, some of which sharing a common path, over an AFDX network, but which are nevertheless segregated at the application layer. US 2014/180504 also acknowledges the move towards Integrated Modular Architecture (IMA) in avionics networks such that general purpose computers, in the form of electronic cards mounted in an IT rack in the avionics bay, perform various avionics functions over an AFDX network but differ from each other essentially by the software that is executed therein.
Improvements to avionics networks, such as networks compliant with Part 7 of ARINC 664 for example, need to be made bearing in mind the avionics context. Network protocols and standards for non-avionic, or general, application are typically poorly suited to use in avionics. The use of networks, which are compliant with Part 7 of ARINC 664, in aircraft control systems has advantages over other standard protocols, for example.
It will be seen that reduction in the mass attributable to wiring of sensors and actuators (hereinafter collectively referred to as transducers) is desirable. There is a desire to further develop the Integrated Modular Avionics (“IMA”) approach and to further decentralize avionics with the use of remote electronics. The use of many different types of hardware, particularly new hardware, in avionics is undesirable however owing to certification requirements, maintenance requirements and the like. If there is a desire to use a new, perhaps improved, type of transducer in an avionics system, those parts of the system that change as a result of the integration of such a new component will need to be certified (re-certified). If there are many intervening pieces of hardware/software that need to be reconfigure/reprogrammed in order to accommodate such a new component, all such pieces of hardware/software may need to be recertified before the new components can be used in service.
Avionics systems also need to be suitable for routine testing on-the-ground during maintenance. Distributing yet more electronic devices remotely from the central avionics bay needs to be balanced with the ability to perform such maintenance and testing. Maintenance may include installation and/or reconfiguring an item of electronic equipment at a location remove from the avionics bay. It may be desirable for dataloading operations to be conducted in performing such tasks. Dataloading operations may also be required to download data retrieved by sensor systems on the aircraft for subsequent (off-line) analysis. Dataloading can be slow and can cause undesirable delays, particularly if dataloading operations need to be performed on an item of equipment, or removable part thereof, off the aircraft, for example in a workshop environment. Dataloading on ground when an item of equipment needs to be configured/reconfigured/programmed or the like typically has to be fully completed before the avionics system can be powered up, potentially causing knock-on delays.
It has been proposed that dataloading controllers, on an aircraft, use a dedicated virtual link and port to multicast what dataloads are available. Subscriber equipment/modules can then respond to this multicast and request a dataloading transaction. Such a proposal utilises two-way communication using both receive and transmit ports and requires all equipment/modules to know the multicast message to subscribe to and which dataloads are needed for the particular equipment/module.
When seeking to make improvements to the avionics network of an aircraft other factors need to be borne in mind. Consideration may need to be given to the overall mass difference introduced by any such improvements. Consideration may need to be given to the increase or reduction in certification requirements introduced by any such improvements. Consideration may need to be given to the overall cost of any such improvements. Consideration may need to be given to the time taken for configuration and ongoing maintenance introduced by any such improvements.
The present invention seeks to mitigate one or more of the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved avionics network and/or an improved aircraft control system. Alternatively or additionally, the present invention seeks to provide an improved means of integrating transducers in a “digital aircraft”. Alternatively or additionally, the present invention seeks to provide an improved means of configuring the network, parts thereof, and/or components/parts attached thereto, of a “digital aircraft” whilst easing certification requirements. Alternatively or additionally, the present invention seeks to provide an improved method of operating and/or reconfiguring an aircraft control system, and/or an improved method of communicating across an avionics network.